1. Technical Field
The present invention relates to connector-less attachments for structural members, and more particularly to a connection between a base substrate of sandwich construction and a load supporting “take-off” member, where large transverse loads can be applied to the base substrate for a wide range of service temperatures, including cryogenic temperatures.
2. Description of the Related Art
Structural connections between a sandwich or honeycomb substrate and another structural member are well known in the prior art. As an example, U.S. Pat. No. 4,671,470 to Jonas discloses a connection between sandwich skin panels and aircraft frame elements using an “H”-shaped woven composite connector. A groove is formed in the panel, and lateral extensions of the connector mid-portion are positioned over adjacent lateral surface regions of the substrate. A structural foam filler is positioned between the lower leg portions of the connector before it is inserted in the groove in the panel. After being positioned in the panel groove, the connector is secured using a bonding agent. The structural foam filler serves the purpose of backing up the connector legs to insure that they make broad area contact with the walls of the groove and enhancing its ability to transfer the shear load across the groove.
Other devices for transferring loads to and from sandwich panel structures include those taught by U.S. Pat. No. 4,800,643 to Higgins (teaches a method for mounting a fastener in a sandwich panel to support a bolt for holding auxiliary structures to the panel), and U.S. Pat. No. 5,093,957 to Do and U.S. Pat. No. 4,981,735 to Rickson (both teach mounting upper and lower disks with co-linear bores in a sandwich panel for the purpose of attaching external structure to the panel via the bores). Other similar devices are disclosed by U.S. Pat. No. 3,510,916 to Phelan, U.S. Pat. No. 3,892,099 to Worgan et al., and U.S. Pat. No. 3,305,996 to Shapiro.
The cruciform of the present invention facilitates easier installation into the sandwich panel as compared with existing art technologies. Installation of the cruciform requires only cutting a slot through the face sheet and core of the sandwich panel. This slot can be accomplished in a single cutting operation that can be performed after the sandwich structure is fabricated. Cutting the slot after the sandwich structure is fabricated provides the flexibility to accurately locate the cruciform on the sandwich panel at a later stage in the assembly process, thereby reducing the effect of assembly and manufacturing tolerance buildup.
By comparison, Jonas, U.S. Pat. No. 4,671,470, discloses a design which requires that a finite-width strip of face sheet and core be removed from the sandwich panel to form a groove for installing the H-shaped connector, or that a groove be prefabricated into the sandwich panel. Removing a strip of core to form a groove is difficult because removal requires that the core strip be severed from the inner face sheet. This operation increases the risk of damage to the inner face sheet. Prefabricating a groove into the panel significantly increases the complexity of the sandwich panel tooling and manufacturing process and greatly reduces the: capability of the design to accommodate the buildup of manufacturing and assembly tolerances.
Embodiments of the present invention avoid these drawbacks and difficulties as herein described.
Against this background, the applicant has developed a novel apparatus and method for securing a structural member to a sandwich panel that will allow transverse take-off loading through the fastener.